\documentclass[10pt]{article} % required
\pagestyle{empty} % required
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{color}
\usepackage[T1]{fontenc}

\begin{document}\definecolor{fgC}{rgb}{0,0,0}\color{fgC}\[\begin{matrix}
 \sigma = 10 \\ 
 \rho = 28 \\
 \beta = \frac{8}{3}
\end{matrix}\]\end{document}